In a solid-state imaging device, phase difference pixels are provided as some of the pixels two-dimensionally arranged in a matrix fashion, and focus detection is performed by a known imaging surface phase difference technique.
The right half or the left half of each phase difference pixel is covered with a light shielding film, and the imaging surface phase difference technique is a technique of detecting a phase difference on an imaging surface between a phase difference pixel that receives light at its right half and a phase difference pixel that receives light at its left half (see Patent Document 1, for example).
In this case, the sensitivity of the phase difference pixels is severely degraded due to a decrease in aperture ratio. Therefore, the phase difference pixels as pixels for generating images become defective pixels, and cannot contribute to signals as images. As a result, image resolution degradation and false color generation are caused due to the influence of the defective pixels. Particularly, in a phase difference pixel as a fine pixel of 1.5 μm or smaller, the aperture size is reduced to ½ of the wavelength Δ. Because of the principles of cutoff frequencies of waveguides, the long wavelength side of incident light is cut off, and sensitivity is severely degraded (the cutoff condition is λ≥2a, where “a” represents the aperture size). This means that a rapid drop in sensitivity is accompanied by degradation in focusing accuracy, particularly in dark places.
To counter this, there is a technique by which a photodiode (PD) is divided into two parts in a pixel, and a phase difference is detected without any light shielding film (see Patent Document 2, for example). In this case, signals from the divided PDs are combined and are used as an image signal. Accordingly, phase difference pixels do not become defective pixels, and sensitivity degradation is prevented.
However, the number of read transistors increases as the PDs are divided. Therefore, manufacturing of fine pixels, or particularly, fine pixels of 1.5 μm and smaller, becomes difficult, because of the structures of those pixels. Also, the decrease in the capacity of each PD has adverse influence such as rapid saturation of the PDs.
For the above reasons, it is safe to say that the light shielding film technique using light shielding films and the PD dividing technique using divided PDs are not suitable for fine pixels.
Meanwhile, there is a technique by which a large on-chip lens (OCL) is formed for more than one pixel, and a phase difference is detected with signals generated from the pixels sharing the OCL (see Patent Document 3, for example).